Rouen: Archbishop Lebrun said "Catholic church cannot take up any other arms than prayer" (Photo: stibou5)

Local police then shot and killed the attackers. Three other people were also injured, one of whom is in critical condition.

The French authorities are treating the incident as a potential terrorist attack, with a bomb disposal squad dispatched to the scene to search for explosives.

Dominique Lebrun, the archbishop of Rouen, said in a statement that the local community was “shocked”.

“The Catholic church cannot take up any other arms than prayer and human fraternity,” he said.

The archbishop was attending a Catholic youth rally in Poland, and urged young people to become “apostles of the civilisation of love”.

He said he would return from Poland immediately.

French president Francois Hollande and interior minister Bernard Cazeneuve also said they were travelling to the crime scene.

Manuel Valls, the French prime minister, said on social media that he was “horrified” by the “barbaric” attack and that all of France stood together with the victims.

French foreign minister Jean-March Ayrault also said France “remained united to face the horror”.

France’s EU commissioner Pierre Moscovici said he was “revolted” and voiced “solidarity with the church and all Catholics”.

The identities of the attackers and their motives were unknown.

But Marine Le Pen, the leader of the anti-immigrant National Front party, said “the modus operandi obviously causes fear of a new attack by Islamic terrorists”.

The jihadist Islamic State group, based in Syria and Iraq, was responsible for an attack in Paris last November that claimed 130 lives.

Tuesday's killing comes shortly after a French man of Tunisian origin killed 84 people by driving a lorry into a crowd in Nice, southern France on Bastille Day, a national holiday.

It also comes after a string of attacks in Germany in recent days - two of them by asylum seekers from Afghanistan and Syria, and one by a German of Iranian origin who admired a far-right killer, the Norwegian Anders Breivik.